hallo guys. this is my first post( welcome me :tongue2: !). Anyway i'm a freshman taking electrical engineering with a keen intrest in physics. anyway my question is this: How do we know that physical constants are really constants. Ok, one way you might say is by assuming, that the quantities are linearly dependant on each other. And then verifying this via experimentation. But how do we know that these are not just linearly correleated at human scales. may be at a quantum level(or stellar sizes) the quantities may vary?(i specifically have G in mind when i talk abt this) any reply will be greatly appreaciated. thankyou.